The present invention relates generally to ultrasonic welding and, more specifically, to an ultrasonic welding apparatus that reduces sonotrode adhesion during the ultrasonic welding process.
Ultrasonic welding of various materials is known. The process involves vibrating adjacent workpieces clamped between a sonotrode and an anvil. Frictional forces occurring between the vibrating workpieces create a bond or weld that occurs at the interface of the adjacent workpieces. Accordingly, various sonotrode and anvil surface configurations, i.e., the surface that contacts the workpieces, are known and used to transfer energy from the sonotrode to the interface of adjacent workpieces. Such configurations attempt to reduce the energy loss at the sonotrode/workpiece interface or the anvil/workpiece interface thereby increasing the energy to the workpiece/workpiece interface and increasing the overall efficiency of the ultrasonic welding apparatus.
Further, it is known that when using an ultrasonic welding apparatus to weld metals, specifically aluminum, the sonotrode or more specifically, the sonotrode tip may stick to the workpiece being welded. The adhesion can be so severe as to damage the weld when detaching the sonotrode from the joined workpieces. Sticking or adhering to the workpiece generally results from the sonotrode sliding on the workpiece. When the sonotrode slides, it causes galling or a buildup of material on the sonotrode tip.
Thus, each time the sonotrode performs a weld, a small amount of aluminum adheres to the sonotrode tip. Continued welding operations result in aluminum build up on the tip. The built up aluminum on the tip bonds with the material of the workpiece. When this occurs, the tip sticks to, or in short, becomes welded to the workpiece. Additionally, as aluminum builds up on the tip, it clogs the gripping surface of the tip and reduces the efficiency of the ultrasonic welding apparatus as energy normally transferred to the workpiece to perform the weld remains at the tip/workpiece interface.
Therefore, there is a need in the art to provide an ultrasonic welding apparatus designed such that it reduces aluminum/sonotrode adhesion during the ultrasonic welding process while promoting energy transfer to the interface of adjacent workpieces.
Accordingly, the present invention is an ultrasonic welding apparatus. configured such that it reduces adhesion between the welding apparatus and the workpiece during the ultrasonic welding process. In one embodiment thereof, the apparatus includes an arcuate shaped sonotrode tip. The sonotrode tip has a plurality of grooves formed therein. The grooves extend perpendicular to the direction of sonotrode vibration. The length and depth of each groove depends in part upon the curvature of the sonotrode tip surface. The sonotrode tip also includes a plurality of lands formed adjacent to the grooves.
In accordance with a further embodiment of the invention, a surface treatment is provided on the sonotrode tip to reduce adhesion of the tip to the workpiece. The surface treatment may include an insert formed of a stick-resistant material placed on the sonotrode tip.
In accordance with a further embodiment, rotation of the anvil of the ultrasonic welding apparatus after the weld is completed operates to release the workpiece from the ultrasonic welding apparatus. Rotation of the anvil may be combined with the use of a sonotrode tip having reduced adhesion properties such that any sticking occurs at the anvil/workpiece interface rather than the sonotrode/workpiece interface.
Accordingly, the ultrasonic welding apparatus operates to reduce or control sticking of the sonotrode to the material or workpiece while having suitable gripping ability to transfer energy from the sonotrode to the workpiece to perform the ultrasonic welding process.